Receiving method and apparatus of analog television signals technical field

ABSTRACT

Receiving method and apparatus of analog television signals where analog television signals receiving is performed by digital processing are proposed. 
     A high frequency signal supplied to an input terminal  1  is supplied to a mixer circuit  2  and mixed with a local oscillation signal from a local oscillator circuit  3 . The intermediate frequency signal from the mixer circuit  2  is supplied to an A/D converter circuit  4 . Thereafter the digital converted signal is supplied to a video carrier wave reproducer circuit  5  and a video demodulator circuit  6  by digital processing, and a demodulated video signal is derived at an output terminal  7 . At the same time the digital signal from the A/D converter circuit  4  is supplied to a phase comparator circuit  11  and phase compared with an oscillation signal from a variable frequency oscillator (VCO)  12  and further the phase compared output is supplied to the VCO  12 . The phase compared output of the phase comparator  11  is additionally supplied to an adder  13  and the video carrier wave component from the video carrier wave reproducer circuit  5  is subtracted. The subtracted output is then supplied to a low pass filter  14  and a demodulated sound signal is derived at an output terminal  15.    
     In this way an analog television signals receiving can be performed by digital processing and can be made common within a digital television receiving means.

TECHNICAL FIELD

The present invention relates to receiving method and apparatus ofanalog television signals where analog television signals can bereceived by digital processing and more particularly to receiving methodand apparatus suitable for being used in a television receiver where,for example, signal proceeding is executed by digital form.

BACKGROUND ART

In an apparatus, for example, receiving analog television signals,analog processing as shown in FIG. 2 has been used in the prior arttechnology. In more detail with reference to FIG. 2, a high frequencysignal supplied to an input terminal 21 is supplied to a first mixercircuit 22 and mixed with a first local oscillation signal from a firstlocal oscillator 23 such that an intermediate frequency signal isformed. The intermediate frequency signal from the first mixer circuit22 is supplied to a video carrier wave reproducer circuit 24 and a videodemodulator circuit 25, and a demodulated video signal is derived at anoutput terminal 26.

At the same time the intermediate frequency signal from the first mixercircuit 22 is supplied to a second mixer circuit 27 and mixed with avideo carrier wave from the video carrier wave reproducer circuit 24. Inthis way a modulated sound signal of stabilized carrier phase is formedand this modulated sound signal is supplied to a sound demodulatorcircuit 28 where a demodulated sound signal is derived at an outputterminal 29. Accordingly video and sound signals included in the highfrequency signal which is supplied to the input terminal 21 aredemodulated and derived at the output terminals 26 and 29 respectively.

In view of the above apparatus, the video modulation system of theconventional analog television signals is a suppressed-carrier amplitudemodulation system and a video carrier wave is reproduced in the videocarrier wave reproducer circuit 24. In this case the signal based onsuch a suppressed-carrier amplitude modulation system has atolerable-characteristic merit in phase noises and/or frequency changes,so that it is possible to derive demodulated video signals at the outputterminal 26 after demodulating in the video demodulator circuit 25 byusing the reproduced video carrier wave.

On the other hand the sound demodulating system of the analog televisionsignals is generally a frequency modulation system which is easilyinfluenced by the phase noises and/or frequency changes. However, in theabove mentioned apparatus video carrier wave reproduced in the videocarrier wave reproducer circuit 24 is supplied to the second mixercircuit 27 where the phase noises and/or frequency changes are cancelledby the phase noises and/or frequency changes included in that videocarrier wave, so that a stabilized signal can be processed.

In this way a stabilized modulated sound signal in which phase noisesand/or frequency changes are cancelled is derived from the second mixercircuit 27 and a signal from the second mixer circuit 27 is supplied toa sound demodulator circuit 28. Accordingly a demodulation is performedin the sound demodulator circuit 28 based on a stabilized modulatedsound signal in which phase noises and/or frequency changes arecancelled, so that it becomes possible to derive a stabilized soundoutput signal at an output terminal 29.

On the other hand, recent years a digital type television broadcastingstarted and digital television receivers which receive digitaltelevision signals have begun spreading. In such digital televisionreceivers the reception, the demodulation and the like are all performedby digital processing. However, it should be noted that analog typetelevision broadcasting is also maintained now, so that it is demandedthat analog television signals can also be received in such digitaltelevision receivers.

For this purpose the conventional digital television receivers areadditionally provided with receiving means for receiving analogtelevision signals by means of analog processing as shown in FIG. 2independently to the receiving means for receiving digital televisionsignals by means of digital processing. However, it should be noted thatnumbers of parts which constitute circuits increase by providing 2channels of such receiving means, so that it causes a problem of highercost and causes a bother for smaller-size's demand, and at the same timeit causes a problem of power-consumption increase and the like.

The present invention has been made in view of such conditions, andproblems to be solved are directed to that, in the conventionalapparatus, receiving means for receiving analog television signals isbased on analog processing such that receiving means for receivingdigital television signals and for receiving analog television signalsshould be independently provided where numbers of parts which constitutecircuits increase, so that it causes a problem of higher cost and causesa bother for smaller-size's demand, and at the same time it causes aproblem of power-consumption increase and the like.

DISCLOSURE OF THE INVENTION

Claim 1 of the present invention is directed to receiving method ofanalog television signals which is characterized in that an intermediatefrequency signal obtained by mixing a high frequency signal with a firstlocal oscillation signal is supplied to a video carrier wave reproducercircuit for reproducing a video carrier wave, the intermediate frequencysignal is supplied to a phase comparator for phase comparing with asignal from a variable frequency oscillator controlled based on thephase compared output, a variable component of the video carrier wavefrom the video carrier wave reproducer circuit is subtracted from thephase compared output so as to cancel the changes of the sound signalcomponent.

In this way the analog television signals reception can be performed bydigital processing and can be formed commonly within the digitaltelevision receiving means.

Additionally, according to claim 2 of the present invention theintermediate frequency signal is A/D converted and digital processing isconducted in the succeeding stages, so that signal processing can beperformed by digital processing.

Further, claim 3 of the present invention is directed to receivingapparatus of analog television signals which comprises a video carrierwave reproducer circuit supplied with an intermediate frequency signalwhich is obtained by mixing a high frequency signal with a first localoscillation signal for reproducing a video carrier wave, a phasecomparator supplied with the intermediate frequency signal for phasecomparing with a signal from a variable frequency oscillator controlledbased on the phase compared output, and an operation means foreliminating changes of a sound signal component by subtracting thevariable component of the video carrier wave derived from the videocarrier wave reproducer circuit from the phase compared output.

In this way the analog television signals reception can be performed bydigital processing and can be formed commonly within the digitaltelevision receiving means.

Additionally, according to claim 4 of the present invention theintermediate frequency signal is A/D converted and digital processing isperformed in succeeding stages, so that signal processing can beperformed by digital processing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram showing a construction according to anexemplified embodiment of a main circuit portion of a televisionreceiver to which receiving method and apparatus of analog televisionsignals of the present invention is applied; and

FIG. 2 is a block diagram to be used for explaining a conventionalanalog television receiver.

BEST MODE FOR CARRYING OUT THE INVENTION

According to the present invention an intermediate frequency signal issupplied to a phase comparator and phase compared with a signal from avariable frequency oscillator which is controlled by the phase comparedsignal, and further, a variable component of a video carrier wavederived from a video carrier wave reproducer circuit is subtracted fromthe output derived from the phase comparator for eliminating thevariation of the sound signal component whereby the receiving of analogtelevision signals is performed by digital processing, so that it can becommonly constituted within the receiving means of digital televisionsignals.

The Present invention will be explained hereinafter with reference tothe drawings and FIG. 1 is a block diagram showing a constructionaccording to an exemplified embodiment of a main circuit portion of atelevision receiver to which receiving method and apparatus of analogtelevision signals of the present invention is applied.

In FIG. 1, a high frequency signal supplied to an input terminal 1 issupplied to a first mixer circuit 2 and mixed with a first localoscillation signal from a first local oscillator circuit 3, so that anintermediate frequency signal is formed. The intermediate frequencysignal from the first mixer circuit 2 is supplied to an A/D convertercircuit 4 and converted to a digital signal, for example, by samplingfrequency of 27 MHz. Thereafter the converted digital signal is suppliedto a video carrier wave reproducer circuit 5 and a video demodulatorcircuit 6 by digital processing and a demodulated video digital signalis obtained at an output terminal 7.

At the same time the digital signal from the A/D converter circuit 4 issupplied to a phase comparator circuit 11 and phase compared with anoscillation signal from a variable frequency oscillator (hereinaftersimply designated as VCO) 12. Additionally this phase compared output issupplied to the VCO 12 such that the oscillation signal of the VCO 12 isvaried based on the phase compared output. In this configuration thephase comparator circuit 11 is operated as a multiplier and an operationis conducted for converting a sound digital signal component included inthe digital signal to a certain frequency.

This is to say, an intermediate-frequency video carrier wave and adigital signal including a sound carrier wave are derived from the A/Dconverter circuit 4. In this situation the reference oscillationfrequency of the VCO 12 is selected, for example, as the sound carrierfrequency such that a digital signal component near this sound carrierfrequency-band is converted to, for example, a frequency near the baseband and derived from the phase comparator 11. It should be noted thatthe derived digital signal here has an influence caused by phase noisesand/or frequency changes.

Accordingly, the phase compared output of the phase comparator 11 isadditionally supplied to an adder (operation means) 13 and the videocarrier wave component reproduced by the above mentioned video carrierwave reproducer circuit 5 is subtracted therein. In this way a sounddigital signal of stabilized carrier phase is formed. In more detail,the video carrier wave component reproduced by the video carrier wavereproducer circuit 5 includes phase noises and/or frequency changessimilar to those included in the digital signal of the intermediatefrequency signal and by subtracting the video carrier wave component,phase noises and/or frequency changes of the frequency converted digitalsignal will be cancelled, so that a stabilized sound digital signal canbe obtained.

Consequently a stabilized sound digital signal where phase noises and/orfrequency changes are eliminated by these phase comparator 11 and adder13 is formed and similar processing is performed as the conventionalsecond mixer circuit 27. Thereafter the sound digital signal which isstabilized in its carrier phase is supplied to a low pass filter 14where signals other than audible band are eliminated or cut out and ademodulated sound digital signal is derived at an output terminal 15. Inthis way video and sound signals included in the high frequency signalsupplied to the input terminal 1 are demodulated and derived at theoutput terminals 7 and 15 respectively.

In the above apparatus the processing in the phase comparator 11 to thelow pass filter 14 is digital processing all the way and the receivingmeans of analog television signals is realized by digital processing.Accordingly it is possible to form analog television receiving meanswhich is intimate with digital television receiving means, so that thecircuit configuration can be made common both for digital televisionreceiving means and analog television receiving means.

As mentioned above, in the exemplified embodiment an intermediatefrequency signal is supplied to a phase comparator and phase comparedwith a signal from a variable frequency oscillator, and further avariable component of a video carrier wave from a video carrier wavereproducer circuit is subtracted from that phase compared output so asto cancel the changes of the sound signal component whereby an analogtelevision signals receiving can be performed by digital processing andcan be made common within a digital television receiving means.

As mentioned above, in a conventional apparatus analog processing isused for receiving analog television signals, such that digitaltelevision receiving means and analog television receiving means must beprovided independently and numbers of parts which constitute circuitsincrease, so that it causes a problem of higher cost and causes a botherfor smaller-size's demand, and at the same time it causes a problem ofpower-consumption increase and the like, while such problems are easilyremoved according to the present invention.

In this way, according to the above mentioned analog televisionreceiving method an intermediate frequency signal obtained by mixing ahigh frequency signal with a first local oscillation signal is suppliedto a video carrier wave reproducer circuit for reproducing a videocarrier wave, the intermediate frequency signal is supplied to a phasecomparator for phase comparing with a signal from a variable frequencyoscillator controlled based on that phase compared output and at thesame time the variable component of the video carrier wave from thevideo carrier wave reproducer circuit is subtracted from that phasecompared output so as to cancel the changes of the sound signalcomponent whereby analog television signals receiving can be performedby digital processing.

In another view according to the above mentioned analog televisionsignals receiving apparatus, there are provided with a video carrierwave reproducer circuit supplied with an intermediate frequency signalwhich is obtained by mixing a high frequency signal with a first localoscillation signal for reproducing a video carrier wave, a phasecomparator supplied with the intermediate frequency signal for phasecomparing with a signal from a variable frequency oscillator controlledbased on that phase compared output, and an operation circuit foreliminating changes of the sound signal component by subtracting thevariable component of the video carrier wave derived from the videocarrier wave reproducer circuit from that phase compared output, so thatanalog television signals receiving can be performed by digitalprocessing.

It should be noted that the present invention is not limited to theexemplified embodiment mentioned above and various modifications can beapplied without departing from the scope of the present invention.

1. A method of receiving analog television signals having video andsound signals, comprising the steps of: mixing a high frequency signalof the received analog television signal with a local oscillation signalto produce an intermediate frequency signal, reproducing a video carrierwave from said intermediate frequency signal, phase comparing saidintermediate frequency signal to a variable frequency signal to producea phase compared output, controlling the variable frequency signal as afunction of the phase compared output, and subtracting a component ofthe reproduced video carrier wave from said phase compared output so asto cancel changes of a sound signal component.
 2. The method of claim 1,further comprising the steps of A/D converting the intermediatefrequency signal, and digital processing the steps of video carrier wavereproduction, phase comparison and subtraction.
 3. Receiving apparatusof analog television signals comprising: a video carrier wave reproducercircuit supplied with an intermediate frequency signal which is obtainedby mixing a high frequency signal with a first local oscillation signalfor reproducing a video carrier wave, a phase comparator supplied withsaid intermediate frequency signal for phase comparing with a signalfrom a variable frequency oscillator controlled based on the phasecompared output, and an operation means for eliminating changes of asound signal component by subtracting the variable component of thevideo carrier wave derived from said video carrier wave reproducercircuit from the phase compared output.
 4. Receiving apparatus of analogtelevision signals according to claim 3, wherein said intermediatefrequency signal is A/D converted, and digital processing is preformedin the succeeding stages.